Turbochargers are generally known and used for increasing power in both internal combustion and diesel engines. Exhaust gas is used to provide energy for a turbine, and the turbine drives a compressor which is typically mounted on a common shaft with the turbine. The compressor receives air from atmosphere, compresses it, and forces the air into the intake manifold of the engine. One feature commonly used in some turbochargers is the concept of variable turbine geometry (VTG). A turbocharger which employs the concept of VTG has the capability of varying the amount of exhaust gas flowing through the turbine, and can vary the amount of exhaust gas flow independent of engine speed.
Assembly of most VTG turbochargers involves the use of a “cartridge,” which is placed in a turbine housing such that the cartridge surrounds the turbine wheel. The cartridge is a circular object typically made of two metal rings which hold together a series of vanes. The angle of the vanes relative to the turbine wheel can be changed, thereby changing the amount of exhaust gas flow through the turbine. Current generation passenger car VTG turbochargers use a Belleville-washer-shaped heat shield to provide a spring load against the cartridge to ensure that the cartridge stays in place during turbocharger operation. This heat shield essentially performs two functions, one is to hold the cartridge in place, and another is to deflect heat from the exhaust gas, preventing damage to various turbocharger components.
One common problem with the heat shield performing the function of holding the cartridge in place is that the heat shield comes in contact with the hot exhaust gas from the engine, and therefore could potentially relax and lose shape. This most often occurs when the turbine wheel is a standard wheel with scallops between the blades. If the Belleville-washer-shaped heat shield relaxes and loses shape, the amount of force applied to the cartridge could potentially be reduced, and the cartridge may no longer be held in the correct position relative to the turbine wheel.
Also, the heat shield occupies a large gap located between the turbine wheel and the bearing which supports the shaft upon which the turbine wheel is mounted. This large gap reduces efficiency if used with the standard wheel having scallops between the blades. The gap could allow oil leakage across the piston ring seal due to reduced pressures between the turbine wheel and heat shield. The gap also requires a relatively large distance between the turbine wheel and the bearing that supports the shaft which could lead to increased efficiency losses due to the required, increased radial clearance between the turbine wheel and turbine housing, and could lead to increased instability for the bearing.
Therefore, there exists a need for a way to hold the cartridge of the VTG turbine in place while resisting heat from the exhaust gases to avoid deformation.